Vacuum type electric circuit breaker

ABSTRACT

A vacuum type electric circuit breaker includes a highly evacuated envelope of electric insulating material and a pair of relatively movable electrodes located in the envelope. At least one of the electrodes has a contact assembly at one end thereof, the contact assembly comprising first and second disc members in parallel. The first disc member being secured mechanically and electrically to the one end of the electrode at its center portion, and the second disc member having a peripheral portion secured to a corresponding peripheral portion of the first disc member. An electric contact is provided at the center area of the second disc member so as to make and break an electric circuit with an electric conductor of the other electrode. There is provided an electric current path in the contact assembly for containing a magnetic field surrounding an electric arc which is established between the contact assembly and the contact of the other electrode and for preventing the electric arc from the dispersion thereof when the electric circuit may be opened by the separation of the contacts.

United States Patent [191 Mizutani et al.

[ June 1 8, 1974 VACUUM TYPE ELECTRIC CIRCUIT BREAKER [75] Inventors: Hirohiko Mizutani, Yokohama;

Osami Morimiya; Shigeo Soma, both of Tokyo, all of Japan [73] Assignee: Tokyo Shibaura-Electric Company,

Ltd., Kanagawa-ken, Japan 221 Filed: Sept. 18, 1972 211 Appl. No.: 289,965

30 Foreign Application Priority Data Sept. 16, 197] Japan 46-71224 52 us. Cl 200/144 200/166 3 [51] Int. Cl. H0lh 33/66 [58] Field of Search 200/144 B, 166 B [56] References Cited UNITED STATES PATENTS 10/1966 Ranheim ..l ZOO/144B 11/1969 Rich 200/144BX Primary ExaminerRobert S. Mac on I Y Attorney, Agent, or FirmOblon, Fisher, Spivak, Mc

Clelland & Maier 57 2 ABSTRACT A vacuum type electric circuit breaker includes a highly evacuated envelope of electric insulating material and a pair of relatively movable electrodes located in the envelope. At least one of the electrodes has a contact assembly at one end thereof, the contact assembly comprising first and second disc members in parallel. The first disc member being secured mechanically and electrically to the one end of the electrode at its center portion, and the second disc member having a peripheral portion secured to a corresponding peripheral portion of the first disc member. An electric contact is provided at the center area of the second disc member so as to make and break an electric circuit with an electric conductor of the other electrode. There is provided an electric-current path in the contact assembly for containing a magnetic field surrounding an electric are which is established between the contact assembly and the contact of the other electrode and for preventing the electric arc from the Y dispersion thereof when the electric circuit may be opened by the separation of the contacts.

2 3 Claims, 7 Drawing Figures PATENIEDJuI is n14 SHEET 1 OF 3 2 VI F 1 VACUUM TYPE ELECTRIC CIRCUIT BREAKER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum type circuit breaker and more particularly to a vacuum type circuit breaker having a new and improved contact assembly for reducing the roughness of contact surface resulting from a high temperature electric are being elongated between electric contacts when in a separated condition.

2. Description of the Prior Art As is well known, vacuum type electric circuit breakers are being widely employed for the safety of good electric power current interruption. There has been a serious problem with such circuit breakers in that severe roughness of the contact surface hasbeen likely to occur due to a high temperature electric arc that is established between the contacts when in a separated condition when an interruption of a large electric power is required.

In order to avoid such a problem, there was known a vacuum circuit breaker having disc-like electric contacts each of which is constructed to spirally form electric current passes directed from a center region to an outer periphery thereof to thereby create loop current passes for causing an electromagnetic field crossing perpendicularly to an electric arc initiated between separated contacts and for electromagnetically driving the arc around the outer peripheral region of the contacts. An example ofsuch vacuum circuit breakers .is shown in U.S. Pat. No. 2,949,520 of Schneider assigned to General Electric Co.

Although a set of circuit breakers have been satisfactorily used to interrupt a large electric power, this system has in the past failed to show distinct reduction of the roughness that occurs on contact surfaces to be separated when the large electric power is interrupted. The roughness of contact surface occurs because when an electric arc is driven around the peripheral region of disc-like contacts by the magnetic field, charged particles in an arc column will be reduced to zero because of considerable release of the charged particles out of the arc column, and accordingly the rate of movement of an electron will be increased to compensate for reduction of charged particles. As a result, the input energy to an annode will increase resulting in numerous spots on the contact surface thereof where the contact surface has melted. Thus, a severe roughness of the contact surface may occur, thus shortening the life of the contacts.

Careful examination indicates that the melting of the contact surface has been defined about the peripheral region thereof, and there sometimes occurs chafing of molten metal in the contact slots thereby bridging the same, such that the contacts have lost the arc driving ability.

There has also been known a type of vacuum circuit breaker in which a coil is wound around an outer wall or enclosure thereof in such a manner as to create a series connection of electrodes to flow an electrical current therethrough. Thus, when an electric arc is initiated between separated contacts, a magnetic field will occur in the axial direction of the electrodes to surround the are for the prevention of rapid dispersion of ions in the arc.

However, in accordancev with such constructions, where a rated current over two thousand arnperes is desired for the circuit breakers, then the size of the whole conductor is substantially increased causing the hole size of the circuit breaker to be enlarged. As a result, the vacuum circuit breaker becomes excessively expensive to manufacture. Further to the above, as the coil conductor is located remote from the arc initiating region, the intensity of the magnetic field surrounding the arc becomes weak to a point where it is insufficient to hold positive current at the desired position with stability.

Another type of vacuum circuit breaker includes a solenoid coil formed at the portion between a contact and one end of an electrode as well as inside of the enclosure. One problem with a vacuum circuit breaker of such construction is that as a coil of large size is enclosed in a highly evacuated envelope, there may unpreferably occur exhaust of gas from the inside of the whole conductor material into the vacuum atmosphere to decrease the vacuum in the envelope-Additionally,

since the magnetic center holds a coil which is located far from the arc initiation region of contacts, the stability of holding the arc decreases similarly to that of the coil mentioned in the prior art.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a vacuum circuit breaker having a new improved contact structure wherein a magnetic field surrounding an electric are initiated between separated contacts can be produced by a contact assembly itself.

Another object of the invention is to provide a vacuum circuit breaker having a new improved contact structure wherein at least one of the contact assemblies is composed of a pair of stacked disc members made of electrically conductive material and each having an electric connection at the outer peripheral portions thereof to make a reversed current flow pass directed radially from a center region to an outer peripheral portion on the disc members such that a magnetic field surrounding an electric are initiated between separated contacts is established by a loop coil for making the reversive current passes.

Another object of the invention is to provide a vacuum circuit breaker having a new improved contact structure wherein each of the stacked disc members holding the contact assembly includes slots directed radially and spirally from a center region to an outer peripheral portion thereof to make loop shaped segments for establishment ofv loop coils through which an electric current to be interrupted can flow.

A further object of the invention is to provide a vacuum circuit breaker wherein a loop coil conductor is disposed between a pair of stacked disc members such that one end of the coil conductor is connected to a point on the outer peripheral portion of one of the disc members and the other end thereof is connected similarly to a point on the outer peripheral portion of the other disc member, such that an electric current to be interrupted can flow through the coil conductor to establish a magnetic field surrounding an are initiated between separated contacts. I

Briefly, in accordance with one aspect of the present invention, these and other objects are attained by the provision of a vacuum circuit breaker in which at least one contact assembly thereof is composed of a pair of disc members made of an electrically conductive material, one of thedisc members being attached to one end of an electrode at the center portion thereof and the other having a contact region at the center portion thereof electrically engaged above with a contact region on another electrode, such that reversed electric current passes are defined to make a loop pass for an electric current to be interrupted and an axis of the loop pass being positioned in parallel with a longitudinal axis of the electrode thereof to establish a magnetic field surrounding an electric are initiated between separated contacts.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention will be easily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is an elevational sectional view of a vacuum circuit breaker embodying the present invention;

FIG. 2 is an exploded, perspective view of a contact assembly, shown in an enlarged scale, of the vacuum circuit breaker in accordance with the present invention;

-FIG. 3 is a contact assembly of FIG. 2 for illustration of electric current flow paths;

FIG. 4' is a photograph of a surface of a contact assembly of FIG. 2 after electric power interruption tests;

FIG. 5 is a similar photograph of a prior art contact assembly after electric power interruption tests;

FIG. 6 isa perspective view of a contact assembly, partly in section, of another embodiment of the invention, and

FIG. 7 is an exploded, perspective view of a contact assembly of a further embodiment in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS through a hole 18 of bottom cover plate 14, and metal lic bellows '19 is provided between electrode 17 and a peripheral edge of the through'hole 18 for prevention of vacuum leakage. Another contact assembly 20 having a similar configuration to that of contact assembly I6 is secured to the upper end of electrode 17. As is well known in the artfa metallic shield 21 surrounds the contact assemblies 16 and 20 and is supported on the inside of cylindrical wall 12 due to the difussion of metallic vapors involved in an electric arc to be initiated between contact assemblies 16 and 20, as more fully described hereinafter.

Since the contact assemblies 16 and 20 have the same configuration in accordance with this embodiment, only assembly 20 is shown in FIG. 2 as an ex ploded view. Contact assembly 20 is composed of two parts, namely a lower disc member 22 welded on an upper end of movable electrode or rod 17, and an.

trode 17 is also welded to the centerpo'rtion on a rear' surface of the disc member 22.

Prior to the pressing process of disc members 22 and 23, spiral slots or throats 25 and 26 are provided on disc members 22 and 23 extending from a center portion to a peripheral portion thereof, and accordingly the disc members 22 and 23 respectively are cut to be divided into a plurality of spiral segments 27 and 28. In the embodiment of FIG. 2, each of disc members 22 and 23 includes four spiral segments 27 and 28.

It can be seen that the spiral segments 27 of upper disc 23 take a clockwise direction, andv the spiral segments 28 of lower disc 22 take a counter-clockwise direction. The disc members 22 and 23 are stacked on each other such that outer peripheral edges 29 and 30 of segments 27 and 28 overlap through their entir length.

Thus, when an electric current flows from contact 24 to electrode 17- through spiral segments 27 and 28 of upper and lower disc members 23 and 22, the electric current will pass first through the spiral segment'27 of upper disc 23 from the inside to the outer edge thereof in a clockwise direction, and will then pass through the spiral segment 28 of lower disc member 22 from the outer edge to the inside thereof in a counter-clockwise direction. i

In this way, it can be seen in the plane view of FIG. 3 that there are provided four loop passes or coils 30, 31, 32, and 33 around the contact region for conducting an electric current to be interrupted, and as a result magnetic fluxes occur as shown by the arrow head in the respective loop coils 30, 31, 32, and 33.

It can be seen in FIG. 1 that the magnetic fluxes as shown by the arrows are in parallel withan axis of an electric are 34 initiated between contact assemblies 16 and 20 and surround the arc to appropriately separate the dispersion of metallic vapors in the are due to difussion. In this way, the electric are 34 will be maintained steadily between the separated contacts during the electric power interruption, and the roughness of the contact surfaces due to severe local heat can be eliminated.

FIG. 4 is a photograph showing a contact surface of a contact assembly of the invention after 30 times of electric power interruption tests of 20,000 amperes,

and FIG. 5 is a similar photograph showing a contact spacer 235 positioned between the edge portions thereof. A downwardly extending portion 236 positioned at the outer end of segment 226 of upper disc 223 is employed for electric connection between the outer end of segment 226 of upper disc 223 and the outer end of the corresponding segment of lower disc 222.

If it will be necessary for the duration of the intensity of the magnetic field to be made by the loop coils of the contact assembly or 200, the area to be surrounded by the loop coils can be derived by the variation of configuration of the throats. I

FIG. 7 shows a contact assembly of a further embodiment in accordance with the present invention. The contact assembly is generally shown by numeral 300 and includes an upper flat disc 323 having a flat contact 324 welded at a center portion thereof, and a tongue member 337 extending downwardly from the outer periphery of the lower surface thereof. A ring insulator 338 includes a notch 339 to receive the tongue 337 therein. A ring conductor 340 includes a notch 34] in the circular direction and a tongue 342 extending downwardly from one rear end thereof. A ring-like insulator 343 includes a notch for receiving-the tongue 342 therein. A flat lower disc 322 is secured to a movable bolt or electrode 317 at the center of a rear surface thereof.

All the parts will be assembled to overlap on each other to form an integral contact assembly 300 such that an electric current flows from upper disc 323 to lower disc 322'. In this case, the current flows straight from upper disc 323 through tongue 337, conductor 340 in the counter-clockwise direction, tongue 342 and lower disc 322 to movable electrode 317.

In accordance with the above embodiments, the conductive ring 340 allows magnetic fluxes to occur in an axial direction of the electrode 317, and accordingly, the magnetic fluxes electrically separate the rapid'dispersion of metallic vapors in an electric are by surrounding and maintaining the arc steady.

From the above, in accordance with the invention, the contact assembly itself functions as a magnetic field coil having a relatively small size and a magnetic center located near the arc region for generating the magnetic fluxes surrounding an electric arc initiated between separated contacts, and thus it is possible to make the vacuum circuit breaker having the less roughness of contacts for prolonging the duty life.

Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described therein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A vacuum circuit breaker comprising:

a highly evacuated envelope;

a pair of co-acting electrodes located in the envelope to be relatively movable from a position of engagement to a position of disengagement to make a cur- 6 cuit interruption;

a contact assembly secured to at least one of said electrodes at one end thereof, said contact assembly including a pair of flat discs one of which has a center portion secured to one end of said electrode and the other of which has a contact region at its center area; said flat discs being electrically connected at the peripheral portion so as to make at least one current loop perpendicular to the axis of said electrode and directed from the center of one of said discs through the outer peripheral portion thereof and theouter peripheral portion of said other disc to the center thereof;

whereby said current loop creates magnetic fluxes surrounding an electric are which occurs between said electrodes during said circuit interruption; and

wherein said one of said flat discs of said contact assembly is spirally cut to make a clockwise current pass, and said other flat disc is spirally cut to make a counter-clockwise current pass.

2. A vacuum circuit breaker according to claim 1, wherein said flat discs include spiral cuts which are overlapped by insertion of a ring insulator located between the outer peripheral edges of said discs.

3. A vacuum circuit breaker comprising:

a highly evacuated envelope;

a pair of co-acting electrodes located in the envelope to be relatively movable from a position of engagement to a position of disengagement to make a circuit interruption;

a contact assembly secured to at least one of said electrodes at one end thereof, said contact assembly including a pair'of flat discs one of which has a center portion secured to one end of said electrode and the other of which has a contact region at its center area; said flat discs being electrically connected at the peripheral portion so as to make at least one current loop perpendicular to the axis of said electrode and directed from the center of one of said discs through the outer peripheral portion thereof and the outer peripheral portion of said other disc to the center thereof;

whereby said current loop creates magnetic fluxes surrounding an electric are which occurs between said electrodes during said circuit interruption; and

wherein said flat discs are constructed by a pair of circular discs whichinclude a conductive ring having a notch in the circular direction thereof and located between said discs and a pair of ring insulators respectively positioned between said discs and the conductive ring, and an electric current path is made from one of flat discs through .one of said conductive ring and the other end of said conductive ring to said other flat disc. 

1. A vacuum circuit breaker comprising: a highly evacuated envelope; a pair of co-acting electrodes located in the envelope to be relatively movable from a position of engagement to a position of disengagement to make a curcuit interruption; a contact assembly secured to at least one of said electrodes at one end thereof, said contact assembly including a pair of flat discs one of which has a center portion secured to one end of said electrode and the other of which has a contact region at its center area; said flat discs being electrically connected at the peripheral portion so as to make at least one current loop perpendicular to the axis of said electrode and directed from the center of one of said discs through the outer peripheral portion thereof and the outer peripheral portion of said other disc to the center thereof; whereby said current loop creates magnetic fluxes surrounding an electric arc which occurs between said electrodes during said circuit interruption; and wherein said one of said flat discs of said contact assembly is spirally cut to make a clockwise current pass, and said other flat disc is spirally cut to make a counter-clockwise current pass.
 2. A vacuum circuit breaker according to claim 1, wherein said flat discs include spiral cuts which are overlapped by insertion of a ring insulator located between the outer peripheral edges of said discs.
 3. A vacuum circuit breaker comprising: a highly evacuated envelope; a pair of co-acting electrodes located in the envelope to be relatively movable from a position of engagement to a position of disengagement to make a circuit interruption; a contact assembly secured to at least one of said electrodes at one end thereof, said contact assembly including a pair of flat discs one of which has a center portion secured to one end of said electrode and the other of which has a contact region at its center area; said flat discs being electrically connected at the peripheral portion so as to make at least one current loop perpendicular to the axis of said electrode and directed from the center of one of said discs through the outer peripheral portion thereof and the outer peripheral portion of said other disc to the center thereof; whereby said current loop creates magnetic fluxes surrounding an electric arc which occurs between said electrodes during said circuit interruption; and wherein said flat discs are constructed by a pair of circular discs which include a conductive ring having a notch in tHe circular direction thereof and located between said discs and a pair of ring insulators respectively positioned between said discs and the conductive ring, and an electric current path is made from one of flat discs through one of said conductive ring and the other end of said conductive ring to said other flat disc. 